We get this question all the time. Here’s all the details.
Q: Which BB Spindle do I need for my new bike using the Profile Outboard Bearing Bottom Bracket?
A: The Short Answer:
- If you have a Mid or a Spanish BB on your BMX Freestyle bike, you need the 5 5/8″ spindle.
- If you have an American BB on almost any style of frame, you need the 5 5/8″ spindle.
- If you are using the Outboard BB and the Spline Drive Sprocket, and you BB shell measures 68mm wide, you need the 5 5/8″ Spindle.
- If you are using the Outboard BB and the Spline Drive Sprocket, and you BB shell measures 73mm wide, you need the 6″ Spindle.
- If you want the narrowest Q factor possible with a 68mm BB shell, get the Internal BB and the 5 1/4″ spindle. This is mostly for track (fixed gear) bikes.
The Longer Answer:
The Spline Drive Sprocket setup will leave you, if you’ve properly centered the spindle, 19mm on each end for the crank arms. The Spline Drive Spider is about 10mm thick, or about 1.5mm thicker than the Sprocket, meaning you’ll have slightly over 18mm of spindle to hold your crank arms with. This is the minimum amount of spindle to properly support your crank arms. It doesn’t hurt to have more spindle inserted into the crank bosses, but you should avoid having less.
The 5 5/8″ spindle is 143mm long- the 6″ spindle is 154.6mm long, so with the 6″ spindle and a 68mm bb shell, you would end up with about 24mm inserted into each crank boss- the splines in each crank boss measures 27.6mm.
If you have a bike with a 73mm BB shell, as many Mountain Bikes do, you are definitely going to want the 6″ spindle. I’ll diagram that one up next time.